Presumably, Robin Hood's Merry Men were deposed Anglo Saxon nobility fighting a losing guerrilla war with the Norman French conquerers. I doubt that they were all that merry in Sherwood Forest when they had to catch and eat wild animals in the dead of winter. They had no microwave ovens, and lived in caves and such. Decent tarps had yet to be invented. Merriness was not a feature of the XI Century.
Today's Klan was a reincarnation of the original Klan founded by Nathaniel Bedford Forrest, which mostly vanished in the 1880's and was resurrected by DW Griffith's film Birth of a Nation as a poorboy racist version of the Elks and Eagles and other lodges, a fraternity for the illiterate who dropped out of the seventh grade. They were not all that merry, either, but they were not hunted by any Sheriff of Nottingham. Some of them managed to get elected as Sheriff of Chattalahootchie County, even. I am sure they were somewhat merrier in those days. But all those Kluxers are gone by now, and what we have is their grandsons, guys who seethe with resentment because they were not hired by Jiffy-Lube or Roto-Rooter.